Distal gold mineralization associated with porphyry system: The case of Hongzhuang and Yuanling deposits, East Qinling, China

Abstract

The Hongzhuang and Yuanling gold deposits are located in the Shiyaogou ore field within the Xiong'ershan area, East Qinling, China, where the ore bodies are hosted in Xiong'er Group and mainly controlled by EW-trending and NE-trending faults. The gold mineralization mechanism and the possible genetic link with the porphyry magmatism and hydrothermal events remain unclear. Here we present results from systematic field investigation, petrographic observation, in situ trace elements and sulfur isotope of pyrite to elucidate the genesis of gold mineralization in these deposits. Based on the occurrences of pyrite in different hydrothermal veins, three types of pyrite are identified from each deposit, including: i) coarse-grained cubic pyrite (HZ-Py1 and YL-Py1) in stage I milky quartz vein; ii) medium- to fine-grained pyrite (HZ-Py2 and YL-Py2) in stage II polymetallic sulfides veins; iii) coarse-grained pyrite (HZ-Py3 and YL-Py3) symbiotic with calcite in stage III quartz-calcite vein. The LA-ICP-MS trace element analyses of pyrite show that Au occurs as invisible nanoparticles or nano-sized inclusions in pyrite through absorption-chemisorption during the growth of pyrite or as nano-sized Au-bearing mineral inclusions. The δ34S values of different generations of pyrite in the Hongzhuang and Yuanling gold deposits range from 3.92‰ to 6.43‰ and 2.82‰ to 4.46‰, respectively, indicating that the ore-forming materials were mainly derived from mantle-related source with affinity to the Late Mesozoic granitic magmatism. The Hongzhuang and Yuanling gold deposits are spatially and temporally correlated with the Shiyaogou pluton and they show consistent material sources. We propose that the hydrothermal Au mineralization in these deposits were the distal products generated from the post-magmatic fluids of the Shiyaogou porphyry system. The stretching and thinning of the early Cretaceous lithosphere led to the upwelling of magma and migration of fluid, forming the Au mineralization in fault structures in the shallow crust.